This invention relates to a method and apparatus for generating an output signal at a preselected time following an input signal. More particularly, the invention relates to a method and apparatus for processing digital signals to generate an output pulse at a predetermined time following the arrival of an input pulse with a time interval delay having a resolution greater than obtainable through direct internal digital clock pulses.
There are numerous applications where it is desired to generate an output signal at a known interval following an external trigger signal. Delayed output signals might be used to initiate measurements arising fron an external event at preselected times following the external event. In another example, precise time lapse photography may be obtained.
Conventional delay pulse generators which are reliable, rugged, and relatively simple stand alone devices do not have an adequate resolution and are typically limited to a resolution of greater than 10 ns from an internal clock frequency of less than 100 MHz. It will be appreciated that circuits operating reliably at 100 MHz are not routinely available from manufacturing lots of electronic components and such circuit components must be individually tested and selected to obtain an acceptable degree of reliability and accuracy.
Reliable circuit operation can be improved by supplying a relatively low frequency pulse train for clocking the operation of digital circuit components. Then, some means are required to interpolate the internal pulse width to improve the resolution. In some instances this interpolation is done using analog techniques, which are subject to conventional output errors from component aging, environmental conditions, and manufacturing tolerances. Other commercial devices use ancillary computers and/or microprocessors to interpolate within a basic internal pulse width. These techniques greatly increase the complexity and cost of a delay timer and decrease its reliability and portability.
It is an object of the present invention to obtain a digital delay unit having a timing resolution less than 10 ns.
Yet another objective of the present invention is to obtain a digital delay unit using components commercially available from manufacturing lots.
One other objective is to obtain a stand alone digital delay unit which is rugged and portable, yet has an output which is presettable with a high resolution.
The problems in the prior art and the above objectives are addressed by the present invention, however, and an improved method and apparatus are provided for digital processing to form an output pulse delayed from an input pulse.